Who are king Arthur's siblings by blood?

King Arthur's primary sibling by blood is Sir Morgause, also known as Morgana, who is often depicted as his half-sister. In some versions of the Arthurian legend, Arthur is also said to have a brother named Sir Kay, though he is sometimes portrayed as more of a foster brother. Another sibling mentioned in certain texts is Sir Gawain, though he is typically considered a cousin. The relationships can vary significantly across different accounts of the legend.